1. Field of the Invention
The present invention relates to an imaging apparatus including an image sensor that generates an image signal of a captured object and a timing signal generation circuit that drives the image sensor. Furthermore, the present invention relates to a method for controlling the imaging apparatus.
2. Description of the Related Art
In general, charge-coupled device (CCD) image sensors and complementary metal-oxide semiconductor (CMOS) image sensors are installed on various imaging apparatuses including digital cameras and digital video cameras. An imaging apparatus equipped with an image sensor includes a timing signal generation circuit that supplies a timing signal (control signal) to the image sensor. The timing signal generation circuit has important roles. As discussed in Japanese Patent Application Laid-Open No. 2002-64753, there is a conventional method for reducing the number of input terminals provided for a transfer electrode drive circuit provided in a CCD image sensor.
However, compared to a CCD image sensor, a CMOS image sensor requires a large number of control terminals to enable an imaging apparatus to operate as intended. The package for a CMOS image sensor is relatively large. The number of terminals substantially determines the outer shape of a package accommodating an image sensor and restricts the chip area of the image sensor.
If the number of terminals provided for an image sensor is large, the number of wiring lines connecting the image sensor to a timing signal generation circuit increases correspondingly. Therefore, the conventional method encounters with the difficulty in mounting constituent parts of an imaging apparatus and determining the layout of the parts. Furthermore, when the number of terminals provided for an image sensor is large, the number of output terminals of the timing signal generation circuit is large. As a result, a package of the image sensor includes numerous pins as much as the number of terminals required. The cost of the package increases.
Moreover, if numerous wiring lines are provided for transmitting control signals to an image sensor that can operate at a higher speed comparable to the CMOS level, a peripheral analog signal (e.g., output signal of the image sensor) may include a noise component. A peripheral circuit (e.g., analog processing circuit, analog-to-digital (A/D) converter, etc.) may operate undesirably due to noise. On the other hand, if the driving ability of a timing signal generation circuit that outputs control signals is decreased, the image sensor may not be driven at a designated speed. Therefore, the image sensor and the timing signal generation circuit are closely disposed to each other. The layout of parts is restricted greatly as described above.
Moreover, a CMOS image sensor may include a timing signal generation circuit and an image sensor formed on the same chip. However, the timing signal generation circuit supplies clock signals not only to the image sensor but also to an A/D converter and a digital signal processor (DSP). Therefore, the clock signal may generate noises having adverse effects on the image sensor. Thus, implementing the above-described conventional method is difficult.